1. Field of the Invention
This invention relates to a tape cassette, such as a video tape cassette, in which a magnetic tape is wound around reels to magnetically record and reproduce electric signals, and more specifically to a tape cassette equipped with a reel brake mechanism.
2. Prior Art
With tape cassettes having a pair of reels around which a length of tape is wound, it is common to provide a pair of brake members which are kept in contact with the reels to prevent its turning lest the magnetic tape should loosen when it is not in use (in storage). When the tape is used the brake members are released to allow free turning of the reels.
Utility Model Application Kokai No. 4-67267 proposes a design which enables a pair of brake members and the related mechanism to occupy only a limited space of a cassette housing. According to the design, a pair of pivotally supported brake members are pressed at one end by springs against serrated peripheries of the reels and, as the release pin of the cassette recorder forces a brake release member upward in the space between the upper and lower casings, the upward motion is transmitted through a cam face to the opposite ends of the brake members so as to unlock them.
In that case a vertical member for guiding the brake release member is formed on the lower casing. As FIGS. 8 and 9 illustrate, the lower casing 40 has guide grooves for the release member formed on a guide wall 41 which also serves as a front wall of the casing, between guide ribs 43, 43 immediately inside of the guide wall 41, and between internal guide members 45, 45. The guide member that guides the brake release member (refer to 8 in FIG. 1) inside the upper casing is thus formed by extending the guide wall 41 of the lower casing into the upper casing 42. The corresponding part of the upper casing 42 is formed with an opening 47.
The part of the upper casing corresponding to the guide wall 41 formed on the lower casing is cut open to provide the opening 47. The opening 47, located in the center of the upper casing 42, makes the upper casing structurally weak.
The inner wall of the upper casing is under constant stress by the spring member (refer to 9 in FIG. 1) that urges the brake release member downward). This can cause bulging of the central part of the upper casing when the cassette is in use at elevated temperature, thereby marring its reliability.
In a tape cassette of the construction described above, the space for holding the brake members is limited because of the structural design of the cassette. There is no room, therefore, to fix the upper and lower casings together with screws in the region where the both casings are constantly under tension by the spring member that normally applies pressure to a brake release lever. Tapping screws are used only in the regions distant from the brake members, i.e., at the front and rear corners and in the center of the rear side.
As described above, the spring member that presses the release lever downward inside the cassette housing also constantly applies upward pressure to the upper casing. This can lead to deformation of the upper casing, causing deviation of the thickness dimension of the cassette out of the specified, standard range or development of a gap between the mating edges at the front of the upper and lower casings, when the temperature at which the cassette is transported or stored is elevated depending on the environment, such as the season of the year or the location as the inside of an automobile.